1. Field of the Invention
The present invention relates to a bearing unit with sensor which detects the condition (including vibration, temperature, rotation speed and the like) of a bearing, a gear box, a spindle or the like incorporated in machinery (for example, a movable body such as a railway vehicle, a car or a guided vehicle, or a mechanical equipment such as a continuous-casting machine or a rolling mill), so that preventive maintenance can be achieved thereon.
In addition, the invention relates to a linear motion unit with sensor which detects the condition (including vibration, temperature, speed and the like) of a ball screw, a linear guide or the like incorporated in a lathe, a machining center, an injection molder, semiconductor manufacturing equipment or the like, so that preventive maintenance can be achieved thereon.
In addition, the invention relates to a wireless sensor attached to an industrial machine or a vehicle such as a car or a railway vehicle so as to transmit signals showing running condition by wireless; a bearing unit or a linear motion unit having the wireless sensor; a management apparatus for receiving the transmitted signals; and a monitoring system using these.
2. Description of the Related Art
Bearings for supporting rotating shafts as axles of vehicle such as cars and railway vehicles, or linear motion units such as ball screws or linear guides and bearings applied to industrial machines such as processing machines or assembling machines may produce vibration (that is, a change of acceleration) due to motion or heat due to friction. Such vibration or temperature does not only affect the lives of the bearings or the linear motion units but also takes part in the accuracy of the industrial machines, the safety of the vehicles, and so on. It is therefore desired to measure the vibration and the temperature appropriately and monitor whether they are in the rated condition. In addition, the rotation speed of bearings is often monitored constantly or reported with constant period because the rotation speed is important to grasp the running condition of apparatus or the like to which the bearings are attached.
Therefore, a general-purpose vibration sensor with an accelerometer, a general-purpose temperature sensor with a thermocouple or the like, a rotation sensor for detecting rotation speed, or the like, is attached to a housing of a bearing or a movable element of a linear motion unit that is a target. Such a sensor is connected to a measuring device through a cable so as to monitor vibration, temperature or the like.
In a related-art bearing unit, for example, as shown in FIG. 30, a temperature sensor 1104 and a rotation speed sensor 1106 are disposed separately and independently on a housing 1102 in which a rolling bearing 1100 has been set. The running condition (a change of temperature, a change of rotation speed, and so on) of the rolling bearing 1100 is detected by the temperature sensor 1104 and the rotation speed sensor 1106.
Actually, the running condition of the rolling bearing 1100 includes not only the change of temperature, the change of rotation speed and the like but also impact vibration caused by an impact load from external force applied to the rolling bearing and abnormal vibration generated with abrasion, flaking, cracking or the like in the rolling bearing by way of example: When only the temperature sensor 1104 and the rotation speed sensor 1106 are provided as in the related-art bearing unit, it takes much time for temperature to be transmitted to a, temperature measuring portion even if abnormality such as flaking occurs in the bearing. Further, when abnormality is slight, it is difficult to detect the abnormality in an early stage of the abnormality occurrence in which the bearing temperature does not increase so much.
In addition, when the temperature sensor 1104 and the rotation speed sensor 1106 are disposed separately and independently, it is necessary to secure a space therefor in the bearing unit. As a result, it is difficult to make the unit compact.
In addition, for example as a railway vehicle, signals of the temperature, the rotation speed and so on detected by the sensors 1104 and 1106 are transmitted to a control unit attached to the vehicle body side 10–20 m distant. Here, the rotation speed signal is a digital signal, and the temperature signal is an analog signal.
However, since the distance between the sensors 1104 and 1106 attached to the bearing unit and the control unit attached to the vehicle body side is 10–20 m, the signals of the rotation speed, the temperature and so on detected by the sensors 1104 and 1106 are easily distorted in their output waveforms or affected by noise due to the signal transmission. Particularly, the analog temperature signal is easily distorted in its output waveform or affected by noise, so as to cause the deterioration of measuring accuracy. In addition, when the temperature signal which is an analog signal is transmitted through a cable together with the rotation speed signal which is a digital signal, noise from the rotation speed signal may be superimposed on the analog temperature signal due to electromagnetic coupling (coupling based on electrostatic coupling, electromagnetic induction or electromagnetic waves).
Further, in such a related-art bearing unit with sensor, for example, as shown in FIG. 31, a vibration sensor 2104 and a temperature sensor 2106 are disposed on a housing 2102 in which a rolling bearing 2100 has been set. The vibration sensor 2104 and the temperature sensor 2106 are connected (wire-connected) to a monitor 2112 and a thermometer 2114 through cables 2108 and 2110 respectively. In this case, changes of condition in vibration and temperature appearing during the operation of the rolling bearing 2100 are detected by the vibration sensor 2104 and the temperature sensor 2106 respectively. The respective detection data is transmitted to the monitor 2112 and the thermometer 2114 through the cables 2108 and 2110. Then, on the basis of the detection data transmitted to the monitor 2112 and the thermometer 2114, a recorder 2116 performs recording/tabulating processing about the vibration condition and the temperature condition, while an alarm device 2118 performs monitoring/alarming processing about the change of vibration and the change of temperature.
In the related art bearing unit with sensor, detection data from the vibration sensor 2104 and the temperature sensor 2106 is transmitted (wire-transmitted) through the cables 2108 and 2110 to the monitor 2112, the thermometer 2114 and so on installed externally. In this case, when the number of the vibration sensors 2104 and the temperature sensors 2106 installed increases, the number of the cables 2108 and 2110 for external transmission has to be increased so much. As a result, the wiring processing of the cables 2108 and 2110 becomes troublesome while the number of parts for the wiring processing increases so that the manufacturing cost of the unit increases. Further, a space for wiring the cables 2108 and 2110 has to be secured in the unit. Thus, the unit increases so much in scale. In addition, when great vibration is given, externally, the cables 2108 and 2110 may be disconnected so that signals cannot be transmitted/received.
In addition, when the bearing 2100 and the housing 2102 move as those in a railway vehicle or a car, the monitor 2112 or a measuring instrument 2116 has to be mounted on the movable body of the railway vehicle or the like.
Further, even in the case of a fixed machine, when the bearing housing 2102 is removed frequently, the cables 2108 and 2110 have to be removed whenever the bearing housing 2102 is removed.
Since there is a limit in the frequency band of vibration waves that can be detected by the vibration sensor 2104 disposed in the related art bearing unit, the vibration waves cannot be detected sensitively when vibration waves generated in the unit are infinitesimal. For example, the related-art vibration sensor 2104 can detect deformation or failure of a member generating comparatively great vibration waves. However, since initial symptoms of abnormal vibration such as infinitesimal deformation, microcrack, abrasion, flaking or peeling appear before the deformation or failure of the member, and the vibration at this time has a form of infinitesimal elastic waves (high frequency vibration) with a high-frequency component of 10 kHz or higher, the vibration condition cannot be detected sensitively. As a result, oven if abnormality begins to appear in the rolling bearing 2100, the symptoms of the abnormality cannot be detected in an early stage. Thus, it is difficult to plan preventive maintenance for the unit.
Particularly, when the rolling bearing 2100 rotates at a low speed, vibration waves generated in the unit become infinitesimal. It is therefore difficult for the vibration sensor 2100 described above to detect the vibration waves accurately. As a result, it is impossible to grasp the abnormality of the bearing in an early stage. In addition, temperature increase in the unit rarely appears in the thermometer, either. Thus, it is impossible to, grasp the symptoms of abnormality such as seizure in an early stage.